A valuable class of curable resins is prepared by reacting an unsaturated monocarboxylic acid with a polyepoxide. Such resins, called vinyl ester resins, can be cured by free radical catalysts or by radiation inducement. When made by the direct esterification of epoxide with acid, there are at least two competing reactions, vis. esterification and epoxy condensation. The latter leads to higher molecular weight vinyl ester resin fractions which increase the viscosity of the product significantly. To meet the rheological requirements of most fabrication methods a high viscosity resin requires increased dilution with reactive diluents. Other problems are also created by the high viscosity. It would be desirable to have a procedure whereby vinyl ester resins of more uniform molecular weight distribution could be prepared.